[tex]\frac{3}{17}+\frac{1}{17}=\frac{4}{17} \\\\ \frac{5}{11} +\frac{6}{11} =\frac{11}{11}=1 \\\\\frac{2}{13} +\frac{7}{13} =\frac{9}{13} \\\\\frac{12}{23} -\frac{1}{23} =\frac{11}{23} \\\\\frac{11}{27} -\frac{4}{27} =\frac{7}{27} \\\\\frac{4}{19} - \frac{4}{19}=0\\\\[/tex]